The invention relates to an adsorption drying apparatus as well as an adsorption drying method, particularly for drying compressed gases.
For drying gases, adsorption methods are frequently used. The dehumidification of compressed air, nitrogen, natural gas or gases from chemical production processes should be mentioned by way of example. Apart from methods using two or more separate adsorption containers which run through a drying cycle and a regeneration cycle in mutual alternation, there are methods working on a rotating adsorbent, in which the adsorbent is fixed within a drum and continuously moved through a sector in which it is regenerated (regeneration sector), and a sector in which it is used for drying (drying sector). On the front sides of the adsorbent, chambers are present through which the various gas flows are passed through the sectors. The sectors are each formed by the parts of a drum situated in the zones defined by the chambers so that each part of the drum is cyclically moved through the sectors.
These methods are often used in air conditioning technology but are also known in compressed air technology. Only by way of example, reference is made in this context to German patent publications DE 1 751 041 and DE 2 238 551. The method according to DE 1 751 041, which is also referred to as a partial stream process, will be explained below on the basis of FIG. 1.
The drying apparatus is in this case configured as a rotatable, drum-like chamber 11 having a plurality of parallel adsorption conduits 101, wherein the adsorption chamber 11 can be moved, preferably continuously, through a drying sector 102 and a regeneration sector 103 using a chamber drive 12.
Part of the gas compressed in a compressor block 2 (a highest stage) of an input compressor 1 is immediately conducted to a regeneration inlet chamber 6 in a drying unit 16, flows then through the regeneration sector 103 of the adsorption chamber 11 to a regeneration outlet chamber 7 while absorbing humidity. The gas stream exiting the regeneration sector 103 is cooled downstream in a regeneration cooler 13 with condensed liquid being precipitated in a separator 14. A main stream is cooled in a secondary cooler 3 of the input compressor 1 with humidity being precipitated in a condensate separator 4.
The main stream and the stream exiting the regeneration sector 103 are unified and conducted into a drying inlet chamber 8. The reunification of the stream exiting the regeneration sector 103 and the main stream is realized according to the prior art by an ejector 15 through which the regeneration stream is sucked in and compressed by the main stream. Since the main stream and hence the reunified stream as well experience a considerable pressure loss due to the secondary cooler 3 and in particular the ejector 15, the regeneration stream is throttled down by a throttle valve 10, prior to entering the adsorption chamber 11 and regeneration chamber 6, to such a degree that a differential pressure between the regeneration inlet chamber 6 and the drying outlet chamber 9 adopts an at least low positive value.
The method according to the prior art is found to be disadvantageous. As a result of the compression in the input compressor, the gas is heated. However, only a minor part of the heat is available for the regenerating, since only the mentioned partial stream is conducted through the regeneration sector. In general, the regeneration capacity within the drying sector is often not sufficient, in particular when larger amounts of humidity have to be adsorbed in the adsorption chamber 11 due to low pressures or high temperatures of cooling media of the heat exchangers used (secondary cooler 3 and regeneration cooler 13). The adsorption chamber 11 is then overloaded and high humidity concentrations occur at the outlet of the adsorption chamber 11. In sum, the method according to the prior art offers a comparatively low operational safety as far as unfavorable conditions are concerned.
Moreover, the ejector 15 is of a comparatively low energy-efficiency. In particular, when a high regeneration flow has to be achieved, a comparatively high pressure loss of the main stream is required to suck in the regeneration stream. The input compressor 1 must then have a correspondingly increased performance so as to secure the required output pressure.
According to the prior art, the ejector 15 is designed for one operating point and is not further regulated. At deviating operating pressures and volume flows, more unfavorable regeneration stream proportions occur.
In particular, when the relative humidity of the gas to be dried amounts to 100%, non-separated drops may be contained. When such drops impact an adsorption material in the adsorption chamber 11, sudden heat developments and material damages arise. The lifetime of the adsorption material is thus comparatively limited.
Methods are known from International patent application publication WO 2005/070518 A1, German patent publication DE 2 311 813 and European Patent EP 1 283 741 B1, in which the compression heat is utilized largely completely by corresponding input compressors by passing essentially the entire gas stream from the input compressor 1 through the respective regeneration sectors. A problem in this case is that a leakage stream occurs as a part of the humid regeneration stream from the regeneration inlet chamber 6 and the regeneration outlet chamber 7 into the drying outlet chamber 9 and/or drying inlet chamber 8, which exhibit lower pressures in the known methods. In the apparatus described in WO 2005/070518 A1, this is prevented by seals (“bulb seals”). During rotation, such seals are exposed to high loads leading to rapid wear and therefore costs. If the seals (“bulb seals”) do not seal entirely, a leakage stream has to be expected all the same. The apparatuses described in DE 2 311 813 and EP 1 283 741 take another approach and try to prevent a contamination of the stream entering into and/or exiting from the drying sector 102 by providing interspaces in which an even lower pressure prevails due to suction. The realization of the latter method is comparatively laborious, with the comparatively high differential pressures within the adsorption chamber putting extremely high demands on the sealing at a drum surface of the adsorption chamber and the mechanical stability of a material from which the adsorption chamber is made. Especially, a high differential pressure between a regeneration zone and the interspace suction involves the risk of high leakage streams which can strongly affect the efficiency of the method.
Furthermore, reference should be made at this point to International patent application publication WO 00/74819 A1, which likewise proposes an adsorption drying method, in which only a partial stream of the gas to be dried is fed to a regeneration sector. Since the regeneration stream, as compared to the non-branched off main stream, experiences a distinct pressure loss after passing through the regeneration sector and a cooler, a fan 48 is provided to enable a reunification of the partial regeneration stream and the main stream. According to the prior art, the fan 48 is hence only necessary because a partial stream is branched off from the main stream and passes separately through the regeneration sector.
In summary, the prior art may be classified into two groups of adsorption facilities and methods. In a first group, only a partial stream is used for regeneration, which reduces the efficiency for the reasons explained above. In a second group, the entire stream is used for regeneration, which, however, either leads to a leakage and hence a lower drying degree that can be achieved, or involves a comparatively high constructional expenditure.